Conventional cine-film cassettes contain a winding reel and an unwinding reel between which the film is accessible at one location in the case of a silent-film cassette and also at a second location, downstream from the first one, in the case of a sound-film cassette. The upstream access serves for the illumination of successive film frames during exposure, as the film is intermittently transported past an image gate behind an objective, whereas the downstream access enables the juxtaposition of a sound track on the film with a recording head.
Since the intermittent motion of the film in the vicinity of the image gate must be converted into a steady one at the recording head, it is desirable to provide separate feed mechanisms at the two locations, such as a reciprocating traction claw and a continuously rotating sprocket wheel. When the constant-speed feed mechanism is operative, i.e. in the presence of a sound-film cassette, proper synchronization of the two drives becomes a problem.